Many weighing applications require that weighing scales be provided in locations where severe environmental conditions exist. For example, large truck and railway scales must be installed outdoors where they are subjected to extremes in temperature, the effects of snow and rain, as well as the effects of dirt, debris, and the shock caused by the successive on-loading and off-loading of heavy moving vehicles. Weighing scales are also required to operate effectively in chemical plants where they are subjected to the action of destructive chemicals in both liquid and solid form. Often, in chemical plants, chemical drums and other containers are filled while they are positioned on the scale platform, and any overflow passes over the scale platform and down into the scale mechanism. In refineries, weighing scales may be subjected to the destructive action of oils and other petroleum products, while in granaries the scale mechanisms are adversely affected by dust and debris.
In the past, vehicle weighing scales have included protective units attached to a scale platform which overlie a scale pit of support frame for purposes of protecting the scale mechanism. For example, U.S. Pat. No. 3,610,352 to Eric Laimins discloses a scale platform with resilient metal plates attached along the sides of the platform. These plates transmit loading forces in the normal loading direction to the scale platform and prevent the application to the platform of adverse side loads. Metal plates of this type which are secured to a scale platform and which overlie the support frame for the scale platform do prove effective for some applications, and particularly for applications wherein electronic load cells of the type shown by the Laimins patent are employed. Although metal plates are subject to the corrosive action of both the elements and chemical environments which renders them unsuitable in many instances, they are additionally responsive to temperature extremes which could alter the forces applied to the platform by the plates. With electronic load cells, some of these problems experienced with metal plates may be alleviated for by electrical and mechanical cell adjustments, but with mechanical lever scales, metal plates attached to the scale platform are totally unsuitable. In a lever scale, as the scale linkages wear, the scale platform tends to move down into a scale pit and also to shift in position relative to the pit walls. Some degree of movement is permissible, but with metal plates attached to the scale platform, movement of the platform relative to the pit wall unbalances the forces applied to the platform by the metal plates. Also, with metal plates which are rigidly secured to the scale platform, it is impossible to inspect the area around the platform between the platform and the pit without laboriously removing the metal plates.
In small, indoor scales, such as bathroom scales, it is sometimes feasible to seal the scale platform to the scale frame by means of a circumferential sealing gasket which is secured to both the platform and frame. Such a structure is shown by U.S. Pat. No. 3,187,826 to T. N. Traff, and the resilient seal shown by this patent operates effectively to seal a small scale to a support frame to repel water. In a small bathroom scale, the Traff sealing unit may be quite efficient, but such a structure is not useful for large truck scales or in destructive environments. Ordinary elastic sealing materials would be rapidly destroyed by rocks and stones driven into the material by truck tires in a truck scale, and extremes in temperature or destructive chemicals will cause the material to crack, deteriorate and harden, losing its elasticity.
In an attempt to protect truck scale mechanisms from the elements, it is common for scale users in the field to "rig" protecting units on the scale structure. Common among these is the use of a thick strip of heavy belting material, such as that commonly used in conveyor belts, which is cut and secured to the edge of the scale pit in spaced relation above the scale platform. This belting material is normally secured to the scale pit by steel strips and fasteners which extend into the concrete wall of the pit, and the belting extends out over the space between the edge of the scale platform and the pit. Although the use of such belting does shelter the intervening space between the scale platform and the pit from the elements, snowplows and other vehicles which come into engagement with this material often destroy the belting and injure the wall of the scale pit. Also, as the scale platform settles with wear in the scale linkage and lever system, rocks and other debris are driven into the space between the belting and the scale platform thereby affecting the accuracy of the weight indication provided by the scale. It is impossible to easily remove this protective belting to inspect and clean the area at the periphery of the scale platform.
It is therefore desirable to provide a scale platform with a peripheral structure which bridges the gap between the scale platform and a scale pit or frame. Ideally, this peripheral structure should provide protection for the scale system while also having elasticity so as to cushion both side-to-side movement and end-to-end movement of the scale platform, thereby providing a secondary checking system. The peripheral structure must also be formed to resist high and low temperatures, shock, elevated pressures, thermal expansion, and a variety of chemical compounds and severe environmental conditions. While surviving exposure to these conditions for prolonged periods, the structure must maintain high compressive strength, crush resistance, and other dynamic and elastic properties, including no significant reduction in compressibility.